Kate Middleton once lost her place at Prince William's birthday to another woman.

Prince William will turn 37 years old on Friday. At present, he is sure to celebrate his special day with his wife and their three children at Kensington Palace because royals usually take a break during their birthdays. However, over a decade ago, his celebration was very different.

Prince William celebrated his 21st birthday in Bucklebury, Berkshire with a big bash. At the time, he had been dating Middleton already. However, his attention was focused on another woman.

"Then at William's party at Windsor Castle later that month it seemed as though Kate was barely registering on William's radar," Katie Nicholl wrote in her 2010 book "William and Harry."

The Duke of Cambridge was reportedly "preoccupied" with a pretty girl named Jecca Craig. Jecca is the daughter of British conservationist Ian Craig and wife Jane. Prince William first met Jecca in 1998 during a holiday on Kenya.

Nicholl added that Prince William had a "secret crush" on Jecca since the first time he met her. Jecca was beautiful and had long blonde hair, deep-blue eyes, and gazelle-like legs. At the event, Middleton lost her place to Jecca.

"As Kate raised her champagne flute to toast the birthday prince at the aptly themed Out of Africa celebration at Windsor Castle, it was Jecca who had pride of place next to William at the head table," Nicholl continued.

Prince William's 21st birthday bash hit the headlines the following day for another reason – a shocking security breach.

Aaron Barshak joined the party and dressed as Osama bin Laden wearing a ballgown. He also made his way to the stage while Prince William was giving a speech and planted a kiss on the prince's cheek.

According to Nicholl on Channel 5's "Royal Scandals," no one realized that something was wrong until Prince William looked at him and said, "Who the hell are you?"

The incident was deemed a "massive security threat" since every senior member of the royal family was in attendance. She added that if a real-life terrorist were present at the time, the royals would have a different story.

Prince William and Kate Middleton
Prince William and Kate Middleton are pictured as they arrive to officially open Dundee’s V&A (Victoria and Albert) museum on Jan. 29, 2019 in Dundee, eastern Scotland. Neil Hanna/AFP/Getty Images